Suddenly, swarms of mysterious flying insects! First, I received a report of robust swarm of airborne bugs in Chilmark. Then another report came from an Aquinnah beach, and finally ace bird photographer Lanny McDowell posted a photo in a Vineyard birding Facebook group of a mockingbird inundated in a small but dense swarm of insects. Though that’s only three such reports, that’s three more than I’ve ever received in one season, and I surmise that this has been a good fall for this phenomenon. Perhaps the recent weather pattern — an extended dry spell followed by several heavy rains — prompted a burst of this activity.
First, it should be noted that lots of types of insects congregate into flying swarms, and they do it for several reasons. In particular, many types of midges (a group within the very large order of flies) often emerge from their larval state at once, in massive hatches. Such swarms are essentially insect singles bars — aggregations of individuals seeking to mate. Or sometimes, intent on feeding rather than flirtation, you may find a swarm of hundreds of dragonflies, convened where air currents concentrate prey.
The recent reports, though, didn’t sound to me like midges, nor yet like dragonflies. Happily, the observer in Chilmark managed to snag a few individuals out of the swarm she observed, and ran them by my office for examination under a dissecting microscope. And Lanny’s photograph showed enough detail of the insects for me to recognize them, in a general kind of way. In both cases, the flying insects were ants.
The idea of ants airborne on their own wings — especially in vast numbers — seems to surprise people, and reasonably so. We think of ants as being in or on the ground, or maybe inside a rotting log. We may admire their numbers or their industrious behavior, but there is nothing about routine ant behavior that would make one expect to see them take flight. And yet period swarming flights are a central part of the biology of most ants.
Here’s the deal. Virtually all of the ants you notice — the ones building ant-hills, scuttling across the pavement, or hauling food back to their colony — are females, though they lack a full set of reproductive apparatus. Inside an ant colony, often deep underground, there will be one or more special females (the number varies depending on species). These are queens, larger than their sister workers and basically optimized for laying eggs to populate the colony. You might say that the whole point of being an ant is to protect your queen, bring her food, tend her offspring, and allow her to reproduce.
But nothing lives for ever, and any species needs to have a way to disperse to new locations. Ants address these challenges by means of mass flights. First, seasonal cues prompt the queen (or queens) to begin producing different kinds of eggs, some hatching into winged males (the only time males are produced), others into queens, large-bodied like their mother but not yet quite ready to begin laying their own eggs.
These new queens also start their lives with wings, and in conjunction with the winged males, launch from the colony into a mass courtship flight. Each queen will mate with one or more lucky male (again, different ant species follow their own rules). The males, created to do nothing more than fly briefly and try to mate, die quickly. The now-fertile queens disperse, find a site for a new colony, and produce their own work force of sterile female workers. Voila! The species is perpetuated.
With a specimen queen from Chilmark adequately magnified, I was able to identify the ant species in that swarm as Solenopsis molesta, a tiny, common, and widespread species sometimes called the thief ant. Typical workers are only a couple of millimeters long; the queen, which I photographed, was about four millimeters long. The species is capable of colonizing a wide range of sites, from in the ground to inside the walls of a house. While Solensopsis often scavenges in natural settings, it can also turn up in homes and kitchens as a “grease ant.”
I have no idea what type of ants were involved in the other swarms; they could have been Solenopsis, too, but about 75 species of ant have been found on the Vineyard, with at least a few more surely not yet detected. Like ants most anywhere, ours are abundant and diverse, and mating swarms are a widespread habit among ants.
The sheer ant-power of their highly cooperative colonies makes them major players as scavengers, predators, and prey. But the main importance of ants may be their engineering prowess — the sheer volume of food they can collect and soil they can move.
Ants are agents for dispersing plant seeds; they break down debris and recycle nutrients; they aerate soil; their colonies host a wide range of parasites or partners, ranging from other ant species to beetles and bees. Mating swarms are an especially obvious sign of these humble insects. But even when they’re out of sight and out of mind, ants carry on with their important work.